The majority of syringes used today for medical or laboratory purposes are disposable and are intended to be discarded after a single use. With the increased awareness concerning the potential for the transmission of the AIDS virus and other infectious diseases, a number of different devices have been proposed to disable the syringe after a single use so that drug abusers or other people may not use the same disposable syringe for multiple injections.
The prior art teaches various methods and apparatuses for disabling the syringe and/or needle so that the syringe may not be reused. A number of these constructions teach the destruction of the inner surface of the syringe barrel as the medication is dispensed from the syringe. A syringe of this type is disclosed in U.S. Pat. No. 4,961,728 granted to Kosinski, wherein a longitudinal locking member having a plurality of radially outwardly directed barb members is mounted on the plunger rod of the syringe. As disclosed in this patent, the barb members allow for a one time withdrawal of the plunger rod proximally in the syringe barrel to a limited maximum volume. As the medication is dispensed from the syringe, the locking member is seated in position along the plunger rod and if the subsequent withdrawal of the plunger rod is attempted, the inner surface of the locking member will engage portions of the plunger rod, while the barb member engage the inner surface of the syringe barrel.
Another approach to solving this problem is disclosed in U.S. Pat. No. 4,961,728 granted to Trenner. The device disclosed in Trenner provides an annular groove near the distal end of the syringe barrel having diameter which is greater than the diameter of the cylindrical inner surface of the barrel. A circular locking element is positioned between the stopper and the plunger rod. The outer diameter of the locking element is larger than the inside diameter of the barrel so that when the plunger rod is moved to the distal end of the barrel, the locking element engages the annular groove and prevents withdrawal of the piston tip from the distal end of the barrel. As disclosed in this patent, if the plunger rod is withdrawn from the syringe barrel when the locking element is seated in the annular groove, the locking element will cause the piston tip to separate from the plunger rod. The use of an annular groove on the inner surface of the syringe barrel effectively eliminates the possibility of having a syringe barrel with a ramp-type of plunger stop near the proximal end of the syringe barrel because the core pin necessary to create the groove cannot be removed from the syringe barrel over a ramp-type member near the proximal end of the syringe barrel.
Although the above-described references provide a single-use syringe which is adequate for most uses, a need remains for a single use syringe which is inexpensive and which may be easily manufactured and assembled.